1. Field of the Invention
This invention relates to an electrosurgical working end and methods for delivering energy to tissue, and more particularly to an instrument working end for grasping tissue that self-modulates energy application to engaged tissues for sealing, welding or coagulating purposes with ohmic heating capabilities together with resistive heating capabilities.
2. Description of the Related Art
In various open and laparoscopic surgeries, it is necessary to coagulate, seal or weld tissues. One preferred means of tissue-sealing relies upon the application of electrical energy to captured tissue to cause thermal effects therein for sealing purposes. Various mono-polar and bi-polar radiofrequency (Rf) jaw structures have been developed for such purposes. In a typical bi-polar jaw arrangement, each jaw face comprises an electrode and Rf current flows across the captured tissue between the first and second polarity electrodes in the opposing jaws. While such bi-polar jaws can adequately seal or weld tissue volumes that have a small cross-section, such bi-polar instruments often are ineffective in sealing or welding many types of tissues, such as anatomic structures having walls with irregular or thick fibrous content, bundles of disparate anatomic structures, substantially thick anatomic structures, or tissues with thick fascia layers such as large diameter blood vessels.
Prior art Rf jaws that engage opposing sides of a tissue volume typically cannot cause uniform thermal effects in the tissue, whether the captured tissue is thin or substantially thick. As Rf energy density in tissue increases, the tissue surface becomes desiccated and resistant to additional ohmic heating. Localized tissue desiccation and charring can occur almost instantly as tissue impedance rises, which then can result in a non-uniform seal in the tissue. The typical prior art Rf jaws can cause a further undesirable effects by propagating Rf density laterally from the engaged tissue to cause unwanted collateral thermal damage.
What is needed is an instrument with a jaw structure that can apply Rf energy to tissue in new modalities: (i) to weld or seal tissue volumes that have substantial fascia layers or tissues that are non-uniform in hydration, density and collagenous content; (ii) to weld a targeted tissue region while substantially preventing thermal damage in regions lateral to the targeted tissue; and (iii) to weld a bundle of disparate anatomic structures.